Securing fasteners

ABSTRACT

A fastener, for example a bone screw, is sized to pass into an aperture of an implant, for example, a bone plate, the fastener having an anchor portion engageable with body tissue, and a head portion formed by an assembly of an insert and an anchor extension. The insert and anchor extension cooperate to form a reduced dimension passable into the aperture, and an expanded dimension not passable out of the aperture. The size of the assembly may be configurable, for example, by tabs, ramped surfaces, or an expanding diameter of a threadable insert.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/291,222, filed May 30, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/117,379, filed May 27, 2011, now U.S. Pat. No.8,771,324. These applications are incorporated by reference herein intheir entireties for all purposes.

FIELD OF THE INVENTION

The invention relates to bone fixation, and more particularly tosecuring polyaxial bone screws within an implant.

BACKGROUND OF THE INVENTION

Bones may be reinforced with rigid structures, for example plates,having apertures through which bone screws, for example polyaxialscrews, may pass. Such reinforcing is useful for addressing fractures orother trauma, correcting alignment, or treating disease. A bone plate isused to span a fracture, or to join different bones. It is importantthat a bone screw securing a bone plate does not loosen and separatefrom the plate postoperatively. This separation or backing out may be aresult of the screws failure to achieve a sufficient purchase in thebone, although the stripping of the screws has also been known to causethis problem, or can be a result of the forces placed upon the screwsfrom spinal movement. Regardless of the cause of the hardware failures,a surgeon must repair or replace the broken or separated parts,requiring an undesirable invasive procedure.

Devices for preventing this separation may be associated with the plateor screw. Examples include a cover positioned over all or part of thescrew head, or an expansion head screw.

SUMMARY OF THE INVENTION

An embodiment of a fastener for securing body tissue relative to animplant, the implant having an aperture with a narrowed entry portion,comprises an anchor portion configured for passing through the apertureand attaching to body tissue; a head portion including an anchorextension and an insert engageable with the anchor extension, the headhaving a plurality of resilient tabs disposed on the anchor extensionand/or the insert and forming a first dimension sized larger than adimension of the narrowed entry portion, the plurality of resilient tabsbendable to form a second reduced dimension relative to the firstdimension, the head portion passable past the narrowed entry portion andinto the aperture when the tabs form the second dimension, and at leastone ramp configured to contact the plurality of resilient tabs and tothereby prevent bending of the plurality of resilient tabs to form thesecond reduced dimension after the head portion has been passed past thenarrowed entry portion into the aperture, the head portion therebyprevented from passing back out of the aperture.

In variations of the embodiment, the insert and the anchor extension areconfigured to mutually engage; the mutual engagement includes a firstflange on one of the anchor extension or insert, and a second bendableflange on the other of the anchor extension or insert, the second flangeoperable when bent to pass over or under the first flange and thereafterto resume an unbent configuration thereby forming an engagement betweenthe first and second flanges; the insert and the anchor extension aremutually engaged prior to the head portion being passed into theaperture; the anchor extension and the insert form a curved exteriorsurface when mutually assembled, the curved surface pivotably engageablewith a curved surface inside the aperture; and the tabs are formed byreliefs disposed between successive tabs, the reliefs forming hingedportions from which the plurality of tabs extend.

In yet further variations, the ramp is configured to bend the pluralityof resilient tabs to form a third dimension at least as large as thefirst dimension; the anchor extension or the insert include a toolengagement profile operative to be engaged by a tool for driving thefastener into body tissue; and the engagement profile forms threeprimary faces.

In a further embodiment, the fastener further includes a threadableengagement between the insert and the anchor extension, the threadableengagement operative to bend the plurality of resilient tabs to form adimension at least as large as the first dimension. In anotherembodiment, the anchor extension includes a ramp, the insert includes aramp, and the anchor extension ramp and the insert ramp mutually engagewhen the anchor portion is moved in a direction back through theaperture to cooperatively increase a dimension of the head portion.

In yet further embodiments, the cooperative engagement causes the insertto expand in diameter; the plurality of resilient tabs are disposed uponthe insert, the insert passable through the narrowed entry portion intothe aperture in a first direction using a first insertion force, andpassable out of the narrowed entry portion in a second direction with asecond force substantially greater than the first force, the insertengageable with the anchor extension to cause the anchor extension to bepassable out of the aperture in the second direction only by applicationof a force at least as great as the second force.

In other embodiments, the at least one ramp is disposed open to each ofthe plurality of resilient tabs, the at least one ramp operative toengage the narrowed entry portion when the fastener is passed into theaperture to thereby bend the resilient tabs; and, the insert is anexpandable ring including the resilient tabs.

An embodiment forming a system for securing body tissue comprises animplant having an aperture with a narrowed entry portion; and a fastenerhaving an anchor portion configured for passing through the aperture andattaching to body tissue; and a head portion including an anchorextension and an insert engageable with the anchor extension, the headhaving a plurality of resilient tabs disposed on the anchor extensionand or the insert and forming a first dimension sized larger than adimension of the narrowed entry portion, the plurality of resilient tabsbendable to form a second reduced dimension relative to the firstdimension, the head portion passable past the narrowed entry portion andinto the aperture when the tabs form the second dimension, and at leastone ramp configured to contact the plurality of resilient tabs and tothereby prevent bending of the plurality of resilient tabs to form thesecond reduced dimension after the head portion has been passed past thenarrowed entry portion into the aperture, the head portion therebyprevented from passing back out of the aperture.

In a variation, the at least one ramp is formed upon the insert, and theaperture includes a ramped interior surface cooperative with the atleast one ramp formed upon the insert to form a close conformingpivotable connection between the implant and the fastener; and, theimplant forms a vertebral plate and the fastener forms a bone screw.

A method of securing body tissue relative to an implant, the implanthaving an aperture with a narrowed entry portion, comprises passing ananchor portion of a fastener through the aperture; attaching the anchorportion to body tissue; engaging an insert with the anchor portion toform a head having a plurality of resilient tabs, the head forming afirst dimension sized larger than a dimension of the narrowed entryportion; bending the plurality of resilient tabs to form a secondreduced dimension relative to the first dimension, and passing the headportion past the narrowed entry portion and into the aperture; andreleasing the resilient tabs to form a dimension at least as large asthe first dimension, wherein the fastener is secured within theaperture. In a variation, a further step includes sliding a ramp of thefastener along the narrowed entry portion to bend the plurality ofresilient tabs.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 depicts a cross-section of a fastener with an anchor extensionhaving bendable tabs, and an internally disposed insert, the fastenerposition prior to passage past a narrowed portion of an aperture in animplant;

FIG. 1A depicts an enlarged view of an indicated region of the fastenerof FIG. 1;

FIG. 2 depicts the fastener of FIG. 1 inserted into the aperture, aninsert not yet fully threaded into engagement with the anchor extension;

FIG. 3 depicts the fastener of FIG. 1, the insert fully threaded intoengagement with the anchor extension;

FIG. 3A depicts an enlarged view of an indicated region of the fastenerof FIG. 3;

FIG. 4 depicts a perspective view of the fastener of FIG. 1, includingan insert not fully engaged;

FIGS. 5-6 depict perspective views of the insert of FIG. 1;

FIG. 7 depicts a perspective view of an anchor extension;

FIG. 8 depicts a top view of the anchor extension of FIG. 7;

FIG. 9 depicts a side view of a fastener including the anchor extensionof FIG. 7 and an anchor portion;

FIG. 10 depicts a perspective view of an insert connectable to theanchor extension of FIG. 7;

FIG. 11 depicts a top view of the insert of FIG. 10;

FIG. 12 depicts a side view of the insert of FIG. 10;

FIG. 13 depicts a perspective view of the fastener of FIG. 9, assembledtogether with the insert of FIG. 10;

FIG. 14 depicts the assembly of FIG. 13 assembled into an implant;

FIG. 15 depicts a cross sectional side view of the assembly of FIG. 14;

FIG. 15A is an enlarged view of a portion of FIG. 15, illustrating analternative configuration;

FIG. 16 is a perspective view of an alternative anchor extension;

FIG. 17 is a top view of the anchor extension of FIG. 16;

FIG. 18 is a side view of a fastener including the anchor extension ofFIG. 16;

FIG. 19 is a perspective view of an insert;

FIG. 20 is a side view of the insert of FIG. 19;

FIG. 21 is a perspective view of an upper side of the insert of FIG. 19;

FIG. 22 is a side view of the insert of FIG. 19;

FIG. 23 is a perspective view of the fastener of FIG. 18 assembled withthe insert of FIG. 19;

FIG. 24 is a top view of the assembly of FIG. 23 assembled into animplant; and

FIG. 25 is a cross sectional side view of the assembly of FIG. 24.

DETAILED DESCRIPTION OF THE INVENTION

In the description which follows, any reference to direction ororientation is intended primarily and solely for purposes ofillustration and is not intended in any way as a limitation to the scopeof the present invention. Also, the particular embodiments describedherein are not to be considered as limiting of the present invention.

One-step locking screw embodiments are disclosed, advantageouslyutilized with an implant, for example a joining member such as a platehaving a fastener or screw aperture, though which an anchor portion of afastener may pass, but not the fastener head. The reduced number ofsurgical steps needed to install the disclosed plates and fastenersadvantageously reduces the overall time and complexity of the surgery,while enabling polyaxial fastener orientation.

The term “backing out” or “back out” herein refers to movement of afastener of the disclosure from a position inserted within body tissue,along a direction reversed with respect to a direction of insertion,whereupon the fastener may be caused to exhibit a reduced fasteningeffect. Back out may be caused by micromotion; disease including tissuedegradation; trauma; or other cause.

Turning now to the drawings, in which like reference numerals refer tolike elements, FIG. 1 shows one embodiment of a fastener 100 includingan anchor 102 portion which engages body tissue, and a head 104 portionextending from anchor 102 which engages a mating implant 200, having anaperture 202. In one embodiment, implant 200 is a plate securable to oneor more bones or bone portions, for example vertebrae, in order tomaintain the bones in a desired relative orientation for therapeuticbenefit of a patient. Implant 200 is provided with an insertion end,through which a fastener of the disclosure is inserted, and an exit 206through which a portion of the fastener may extend, but which is sizedtoo small to prevent passage of head 104.

Implant 200 may have any shape or purpose, and may include, for example,plates, rods, bars, joint replacements, or other anchoring members, andmay be used to join body tissues anywhere in the body. Applications forthe instant disclosure include stabilizing any vertebrae, for examplecervical, thoracic, or lumbar vertebrae; joining bone fractures; joiningsoft tissue, for example tendons or ligaments, to bone; or any procedurehereinafter developed, which advantageously benefits from a reliableanchor connection, and particularly for a polyaxial screw anchorconnection.

To engage fastener 100 to implant 200, anchor 102 is passed through anaperture 202 in implant 200, by any known or hereinafter devised means.For example, anchor 102 may be passed into a preformed opening in bodytissue, or may form or expand an opening in body tissue by self drillingand or self tapping. Threads 106 are advantageously provided to engagebody tissue, for example cortical bone, cancellous bone, tendinous,ligamentous, or other body tissue capable of being securely engaged bythreads. Alternatively, a separate fastener, not shown, for example anut, may engage anchor 102. In accordance with this disclosure, anynumber of fasteners 100 may be passed through any number of apertures202, in any number of implants 200. Head 104 is provided with toolengagement means, for example a Phillips, hex, or other engagementprofile 108, whereby a tool may be used to position and or drivefastener 100 into engagement with implant 200 and or body tissue.

Fastener head 104 is configured to change a dimension from a firstresting maximum dimension to a second expanded maximum dimension. Head104 is further sized and dimensioned to be passable at least in partinto aperture 202. Fastener head 104 is further configured to form acompressed dimension which is advantageously sized to be passablethrough a minimum dimension at an entrance 204 of aperture 202, but toolarge to be passable through an exit 206 of aperture 202. In thismanner, fastener 100 may securely connect implant 200 relative to a bodywhen anchor 102 is engaged with tissue of the body. In FIG. 1, aconfluence of a resting dimension of head 104 and a minimal dimension ofaperture 202 are indicated by arrows “A”. Entrance 204 is advantageouslychamfered to facilitate entry of fastener 100 into implant 200. Plate200 additionally includes a reduced dimension located on an oppositeside to an entrance 204, at an exit 206 to implant 200, operative toprevent fastener heads of the embodiments herein from passing throughimplant 200.

Head 104 is configured to change from a resting maximum dimension to anexpanded maximum dimension by being provided with one or more reliefs110, one of which is visible in FIG. 4. In one embodiment, head 104forms an increased diameter in an expanded maximum dimension. In theembodiment of FIGS. 1-6, a threaded insert 140 is sized and dimensionedto be passed into an opening in head 104, and to thereby expand head 104from the resting maximum dimension to the expanded maximum dimension.Insert 140 includes an increasing diameter from a leading end to atrailing end, and thereby operates to expand head 104 during itsintroduction thereinto. The increasing diameter may be associated with aramping or increase in a core or body of insert 140, or an increase inthread height, as more fully described below.

Reliefs 110 divide head 104 into separate tabs 112 which, due to thereliefs 110, may more easily resiliently bend and deflect radiallyoutwards from an axial center of fastener 100, and thereby increase amaximum dimension of head 104 to a dimension at least as large as theresting maximum dimension, and advantageously substantially larger thansaid resting maximum dimension.

With reference in particular to enlarged view FIG. 1A, head 104 isprovided with threads 114 which cooperate with threads 144 of insert140. Insert 140 may be preassembled by being partially threaded intohead 104 as part of a manufacturing process, prior to surgery, or in theoperating theatre. When fastener 100 has been inserted and head 104 hasbeen positioned within aperture 202, insert 140 may be rotated to expandhead 104, and to thereby fixedly bind head 104 in a set position withinaperture 202.

It is advantageous for the thread pitch of threads 114 and 144 to besubstantially the same, although where sufficient expansion may beachieved through a limited amount of rotation, this is not always arequirement. In addition to an expanding diameter, a thickness ofthreads 114 and or 144 may increase, to provide additional strength, andto increase friction between insert 140 and head 104 to thereby decreasea likelihood of insert 140 backing out of engagement with head 104. Athickness of threads 114 and or 144 in this embodiment is characterizedby an increased width measured along an axis lying along a direction ofinsertion of insert 140, as indicated by region “B” in FIGS. 1A and 5.

Referring again to enlarged view FIG. 1A, and to FIG. 3A, to furtherincrease friction between an inserted or seated insert 140 and head 104,and to expand head 104 from a resting maximum dimension to an expandedmaximum dimension, an interference fit is advantageously formed betweenan upper external diameter 146 of insert 140 and an upper internaldiameter of head 104. The interference fit operates to force tabs 112outwardly to increase a maximum dimension of head 104, due tointroducing an increased overall diameter of insert 140 at externaldiameter 146. A bevel or chamfer may be provided adjacent to respectiveareas 116, 146 to promote smooth formation of the interference fit. Itshould be understood that an interference fit may be similarly formedanywhere along a mating interface between insert 140 and head 104.

Additionally, threads 144 may be provided with a ramped or an increasingdiameter, or increasing thread height. Thread 114, 144 height in thisembodiment is measured radially with respect to an axis of rotation ofinsert 140, as indicated by region “C” of FIGS. 1A and 5. Initially, areduced thread diameter enables head 104 to conform to a compresseddimension when insert 140 is inserted within head 104, as illustrated byarrows “D” in FIG. 3, and as described more fully below. Additionally,an increasing diameter of threads 144 may operate to force tabs 112outwardly to increase a maximum dimension of head 104, due to anincreasing overall diameter of insert 140 as taller thread 144 areas areengaged, as insert 140 enters further into head 104. Alternatively or inaddition to an increasing height of threads 144, threads 114 of head 104may be provided with an increasing height, with like results.Accordingly enlarging of head 104 to form a secure engagement withimplant 200 may be created by either engagement areas 116, 146, threads114, 144, or both.

Head 104 may be provided with a gapped region 118 free of threads, sizedto enable unrestricted passage of threads 144 of insert 140, wherebywhen insert 140 is fully seated, as shown in FIG. 3, insert 140 mayrotate freely. In this manner, excessive tightening of insert 140 may beprevented.

Slight or limited resistance to insertion of head 104 into aperture 202may be created by providing a reduced dimension “A” along a portion ofaperture 202, for example at the region indicated by arrows “A” inFIG. 1. The reduced dimension “A” is smaller than the resting maximumdimension of head 104, thereby forming an interference fit. Accordingly,during insertion, tabs 112 deflect radially inwards towards a centrallongitudinal axis of fastener 100, due to engagement with the reduceddimension “A”, thereby creating a compressed dimension of head 104enabling transmission of head 104 past reduced dimension “A”. Dependingupon the desired degree of interference, a tactile and or audiblefeedback may be provided for a slight interference, or substantial forcemay be required, substantially contributing to a resistance to backingout of fastener 100. A tactile or audible feedback is created byexpansion of head 104 from a compressed state to a resting or expandedstate, and may be due in part to portions of head 104 striking implant200 during this expansion.

To enable polyaxial movement, head 104 may be provided with a curvedouter surface mateable with a curved inner surface 220 of aperture 202.The curved surfaces 120, 220 advantageously conform after head 104 hasbeen expanded to a maximum expanded dimension, thereby maximizing anarea of engagement between respective surfaces 120, 220. Surfaces 120,220 may advantageously be provided with a texture or coating whichenhances friction and improves a frictional bond between head 104 andaperture 200. In addition to, or in lieu of tactile feedback, insert 200may be provided with one or more colored rings, or printed or etchedmarkings, along area 146, to provide a visible indicator of a depth towhich insert 200 has been driven into head 104. For example, a coloredor marked portion may be obscured to indicate sufficient depth.

In use, implant 200 is positioned in a therapeutic location in the body,and body tissue is approximated or otherwise positioned to bestabilized. Insert 140 may be loosely positioned within head 104, or maybe inserted later. If pre-positioned, a driving tool (not shown) ispassed through insert 140 and into a mating recess or tool engagement108 in fastener 100. Fastener 100 may be positioned through aperture 104before or after connecting a tool, after which the tool is used toengage fastener 100 with body tissue. If insert 140 has not yet beenassembled into head 104, it is advantageously assembled before head 104passes reduced dimension “A” along a portion of aperture 202, but mayalso be assembled after. A driving tool is then used to completeengagement of fastener 100 with body tissue, after which the tool iswithdrawn from direct engagement with head 104, but may be left inengagement with a tool engagement profile 148 of insert 140. It is not arequirement that the same tool drive insert 140, although it may reduceinstallation time if profile 148 is so configured. Insert 140 is thenrotated to expand head 104 as described above, thereby securing fastener100 with respect to implant 200.

Referring now to FIGS. 7-15, an alternative fastener 400 has flexibletabs 412 positioned upon insert 440. Head 404 extends from anchorportion 402, and is provided with gapped regions 418 sufficiently wideto render a maximum resting dimension of head 404 substantially smallerthan if gapped regions 418 were not present. In this manner, head 404may be inserted into aperture 202, and may pass reduced dimension “A”along a portion of aperture 202, without a requirement of deflection ofthe ungapped circumferential portions 422 of head 404.

At least one of tabs 412 of insert 440 are sized and dimensioned tooccupy gapped regions 418 of head 404. Insert 440 is positionable uponhead 404, and has a relaxed maximum dimension that is larger thanreduced dimension “A” along a portion of aperture 202; accordingly, themated combination of insert 440 and head 404 has a relaxed maximumdimension that is larger than dimension “A”. Three gapped regions 418and three tabs 412 are illustrated, although it should be understoodthat a different number of mating gaps and tabs may be provided whileremaining within the spirit and scope of the disclosure.

As insert 440 is inserted into aperture 202, tabs 412 deflect radiallyinwards due to engagement with the reduced dimension “A”, therebycreating a compressed dimension of insert 440, enabling transmission ofinsert 440 past reduced dimension “A”. As with embodiment 100, 140, head404 and insert 440 may be preassembled. In the embodiment of insert 440,however, a tool (not shown) directly engages insert 440 at toolengagement 448, and through interaction of tabs 412 and circumferentialportions 422, drives fastener 400 through aperture 202 and into bodytissue. Accordingly, insert 440 is advantageously preassembled into head404.

To enhance retention of insert 440 upon head 404, an insert retainer 450engages a head retainer 452, in this embodiment having a form of matinghook portions, at least one of which is resiliently deflectable toenable engagement. Retainers 450 and 452 are advantageously formed asportions of a circumference of insert 440 and head 404, respectively. Asmay be seen in FIGS. 10 and 12, insert retainer 450 is provided as aflange with a gapped region 454 which enables retainer 450 toresiliently bend or deflect to pass over retainer 452, although itshould be understood that a similar gapped region 454 may alternativelyor additionally be provided upon retainer 452.

Advantageously, assembly of insert 440 and head 404 produces sensedfeedback, including for example an audible, visual, or tactilesensation. A colored band, printed marking, or etched marking may beprovided upon retainer 450 and or 452 to indicate whether a propermating assembly of insert 440 and head 404 has taken place. For example,the visible marking is obscured when proper assembly has occurred.

The embodiment of FIGS. 7-15 further illustrate that fastenerembodiments of the disclosure may be provided with a canulation 456,through which a k-wire, drill, or other fastener or tool may be passed.Additionally, insert 440 is provided with a triangular tool engagementregion, which provides for a positive and secure tool engagement, whileproviding additional protection against stripping of engagement 448, dueto the larger and deeper tool engagement faces afforded by providingthree primary engagement faces, as opposed to, for example, the sixsmaller faces that would be found in a hex engagement. Additionally,anchor 402 may be provided with self tapping or other cutting profile424 or anchoring means as would be understood by one skilled in the art.

To enable polyaxial movement, head 404 and insert 440 may be providedwith ramped or curved outer surfaces 422, 442, respectively, mateablewith a curved inner surface 220 of aperture 202. The curved surfaces422, 442 advantageously conform to curve 220 after the assembly 404, 440has been inserted into aperture 220, and after tabs 412 have beenexpanded to a maximum expanded dimension, thereby maximizing an area ofengagement between respective surfaces 442, 422, and 220. Surfaces 422,442, and or 220 may advantageously be provided with a texture or coatingwhich enhances friction and improves a frictional bond between head 404,insert 440, and aperture 200. In addition to, or in lieu of tactilefeedback, head 404 and or insert 440 may be provided with one or morecolored rings, or printed or etched markings along areas 412, 442,respectively, to provide a visible indicator of a depth to which anassembly 404, 440 has been driven into aperture 202. For example, acolored or marked portion may be obscured to indicate sufficient depth.

With reference to FIGS. 15 and 15A, a terminating ledge 426 abuts anunderside 428 of tab 412. If fastener 400 becomes loose, backs out, oris otherwise forced backwards out of aperture 202, ledge 426 willcontact underside 428 and urge tabs 412 into engagement with curvedinner surface 220 of aperture 202, thereby resisting backing out offastener 200. In particular, during insertion, reduced dimension “A”applies a compressive force at an end of tab 412 which is distal from apoint of attachment, or hinge 458, and therefore there is substantialbending leverage obtained due to the length of tab 412. A force to backout fastener 400, however, causes hinge 458 to be acted upon atdimension “A” directly, without benefit of leverage, and thereforefastener 400 cannot, as a practical matter, be forced out, absentapplication of a tool (not shown). For example, a tool may be providedwhich connects to head 404 or anchor 402 at a location apart from tab412, and which has a component which is moveable relative to theconnection, for example a threadably attached ring, which may be causedto bear upon tabs 412 to operate hinge 458 to reduce a maximum dimensionof fastener 400, thereby enabling removal.

In an alternative embodiment shown in FIG. 15A, representing an enlargedand alternative rendering of a portion of FIG. 15, ledge 426A andunderside 428A are provided with complementary angled slopes whichfurther urge tabs 412 into engagement with inner surface 220, inresponse to a reversing force acting upon fastener 400.

A further embodiment is illustrated in FIGS. 16-25, in which head 604extends from anchor portion 602, and is provided with a tapered surface630, cooperative with a mating tapered surface 650 of insert 640. Inthis embodiment, insert 640 is positioned about an outer surface of head604, and engages curved surface 220 of implant 200 along a complementarycurved surface 642. Insert 640 forms resilient tabs 612 separated byinsert reliefs 610. In this embodiment, reliefs 610 are formed uponalternating faces of insert 640, thereby forming hinges 658, enabling adiameter of insert 640 to enlarge and reduce.

With reference to FIGS. 18 and 20, in particular, head 604 is providedwith a retainer 652 operative to retain insert 640 in engagement withhead 604. In the embodiment of FIGS. 16-25, retainer 652 is formed as anintegral flange disposed along an upper circumference of head 604,although retainer 652 may be separately attached. Insert 640advantageously has a retainer 654 that is formed as a ledge orcooperating shape with respect to retainer 652, whereby retainers 652and 654 are thereby adapted to abut and or mate and thereby resist thepassage of one over or under the other.

To assemble insert 640 onto head 604, insert 640 is passed over retainer652, insert 640 expanding through bending of hinges 658, and afterpassing completely over retainer 652, resiliently resuming a formerrelaxed shape with a smaller diameter, and becoming thereby preventedfrom separating from head 604. The assembled head 604 and insert 640 maythereafter be assembled into aperture 202 by inserting the assembly pastreduced dimension “A” along a portion of aperture 202, as described morefully below.

With reference to FIG. 20, insert 640 defines an insertion or leadingend 660 and a trailing end 662. A first ramped surface “E” extends fromleading end 660 and has a generally increasing diameter along an axisextending from leading end 660 in a direction of trailing end 662. Asecond ramped surface extends from trailing end 660 and has a generallyincreasing diameter along an axis extending from trailing end 660 in adirection of leading end 660. Ramp “F” has a steeper or more rapidlyincreasing diameter than shallower ramp “E”. Ramps “E” and “F”advantageously, but not necessarily, extend circumferentially aboutinsert 640. Ramped surfaces “E” and “F” matingly engage curved surface220, thereby enabling polyaxial movement of fastener 600.

During insertion into aperture 202, insert 640 is initially urged byengagement with dimension “A” away from anchor 602 towards an end ofhead 604, until further movement is arrested by retainer 652.Subsequently, ramp “E” of outer surface 642, and curved surface 220,slide in mutual engagement, creating pressure which causes a contractionof insert 640, bending hinges 658 to reduce a diameter of insert 640,whereby insert 640 together with head 604 are sized to be passablethrough dimension “A”.

After the assembled head 604 and insert 640 lie within aperture 202,curved inner surface 220 and curved outer surface 642 of insert 640cooperate to prevent fastener 600 from backing out. More particularly,as fastener 600 moves in a direction reversed with respect to aninsertion direction, insert 640 moves towards anchor 602 and advancesalong tapered surface 630, whereupon ramp “E” becomes wedged or pinchedbetween curve 220 and tapered surface 630 of head 604, binding insert640 against head 604 with increasing force, and progressively preventingfurther backing out of fastener 600. Should ramp “F” be driven againstreduced dimension “A” at any time, the steep angle of ramp “F” isblocked by reduced dimension “A”, and implant 640 is further driven intothe aforedescribed wedged configuration.

To enable polyaxial movement, curved outer surfaces defined by ramps “E”and “F” advantageously cooperatively mate or conform to curved innersurface 220 of aperture 202. Surfaces 642 and or 220 may advantageouslybe provided with a texture or coating which enhances friction andimproves a frictional bond between head 604, insert 640, and aperture200. In addition to, or in lieu of tactile feedback, head 604 and orinsert 620 may be provided with one or more colored rings, or printed oretched markings upon surface 642 respectively, to provide a visibleindicator of a depth to which an assembly 604, 640 has been driven intoaperture 202. For example, a colored or marked portion may be obscuredto indicate sufficient depth.

Fasteners 100, 400, 600 of the disclosure may inserted or screwed intobody tissue at any desired angle, and therefore need not be insertedperpendicular to a surface of implant 200. The curved or sphericalproperties of head 104, 404, 604, including a combination with implant440 or 640 and the spherical curvature of aperture 200, cooperate toreduce the incidence of a fastener of the disclosure from backing out.More particularly, the largest diameter of the head of the screw islarger than the diameter of the narrowest portion of the opening in thetop our outer side of implant 200, through which the screw head has beenplaced.

The extent of interference between the fastener head diameter and thenarrow opening (diameter “A”) may be different depending on the size ofthe plate, openings, and fastener heads being used. For example theinterference difference between the fastener head and the narrowestopening of implant 200 may be about 0.01 mm or greater, about 0.03 mm orgreater, or about 0.10 or greater, or even about 0.20 mm or greater.Alternatively, the interference between the fastener head and the narrowouter opening may be described relative to the outer diameter of thefastener head itself. For example, the interference may be about 0.5% orgreater of the diameter of the fastener head, about 5% or greater of thediameter of the fastener head, or even about 10% or greater of the outerdiameter of the fastener head. Advantageously, the interference is lessthan about 40% of the outer diameter of the fastener head, for increasedreliability and strength.

While an incidence of backing out is prevented or reduced in likelihoodin accordance with the disclosure, rotation of anchor 100, 400, 600within aperture 202 is not prevented. One advantage of allowing thefastener to rotate freely is that the implant, for example a bonefixation plate, is able to accommodate for movements in the bones, forexample the vertebrae, and to or accommodate for compression of any bonegrafts that have been placed between stabilized bones. An advantage ofallowing the screws to be inserted at any angle is that a relativelyclose spacing of the screws is enabled, without the risk of mutualinterference.

During insertion, when a fastener head of the disclosure interferes withan implant of the disclosure at an interference point, a slightresistance is generated relative to a backing out force. The availableforce of insertion easily overcomes this resistance. When the fasteneris advanced past an interference point, a snap may be perceived as thefastener head moves into a sliding fit area and is allowed to expand andmove more freely. The forces which can cause a fastener to back out fromthe implant are advantageously insufficient to pass the fastener headback past the interference section. In an embodiment, a set screw may beused to further prevent backout of the fastener. In other embodiments,the head of the fastener may be separately clamped to prevent rotation,when such a restriction on the movement of the fastener is desirable.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention.

All references cited herein are expressly incorporated by reference intheir entirety. In addition, unless mention was made above to thecontrary, it should be noted that all of the accompanying drawings arenot to scale. There are many different features to the present inventionand it is contemplated that these features may be used together orseparately. Thus, the invention should not be limited to any particularcombination of features or to a particular application of the invention.Further, it should be understood that variations and modificationswithin the spirit and scope of the invention might occur to thoseskilled in the art to which the invention pertains. Accordingly, allexpedient modifications readily attainable by one versed in the art fromthe disclosure set forth herein that are within the scope and spirit ofthe present invention are to be included as further embodiments of thepresent invention.

What is claimed is:
 1. A method of securing body tissue relative to animplant comprising: positioning an implant having an aperture adjacentto a bone member; inserting a fastener having a head portion and ananchor portion into the aperture such that the anchor portion isinserted into the bone member and the head portion is retained in theaperture, wherein the head portion comprises one or more gapped regionsthat are cut through an upper surface of the head portion; and rotatingan insert positioned within an opening in the head portion of thefastener to a locked position, wherein the insert includes one or moretabs, each of which at least partially occupies the one or more gappedregions such that the one or more tabs are at least partially positionedin the one or more gapped regions in the locked position.
 2. The methodof claim 1, wherein the insert further comprises an insert retainer thatengages a head retainer of the head portion of the fastener, and whereinthe insert retainer comprises a flange with a gapped region whichenables the insert retainer to resiliently bend or deflect to pass overthe head retainer.
 3. The method of claim 1, wherein at least a portionof the head portion has a first diameter and at least a portion of theinsert has a second diameter, the first diameter being smaller than thesecond diameter.
 4. The method of claim 1, wherein the one or more tabsextend the entire length and width of the one or more gapped regions. 5.The method of claim 1, wherein the insert is positioned in an unlockedposition when the one or more tabs are not positioned in the one or moregapped regions.
 6. The method of claim 1, wherein the one or more tabsof the insert are flexible.
 7. The method of claim 1, wherein the insertis preassembled into the head portion of the fastener.
 8. The method ofclaim 7, wherein the insert is compressed as the insert passes throughthe aperture of the implant.
 9. The method of claim 8, wherein theinsert expands after the insert is compressed as the insert progressesfurther downward into the aperture.
 10. The method of claim 1, whereinthe insert has an upper diameter that is greater than a lower diameterof the insert.
 11. The method of claim 10, wherein the upper diameter isprovided by increasing a thread height of threads that extend around theinsert.
 12. The method of claim 1, wherein the insert comprises outerthreads and the head portion of the fastener comprises inner threadsthat engage the outer threads.
 13. A method for preventing back out of afastener comprising: positioning a plate member having an apertureagainst a bone member; inserting a fastener having a head portion and ananchor portion into the aperture, wherein the anchor portion is insertedinto the bone member and the head portion is engaged with the plate,wherein the head portion comprises one or more gapped regions that arecut through an upper surface of the head portion, and wherein the one ormore gapped regions extend circumferentially around the head portion ofthe fastener; and moving an insert positioned in an opening in the headportion of the fastener to a locked position, wherein the insertincludes one or more tabs, each of which occupies the one or more gappedregions such that the one or more tabs are inserted into the one or moregapped regions in the locked position.
 14. The method of claim 13,wherein the insert further comprises an insert retainer that engages ahead retainer of the head portion of the fastener, and wherein theinsert retainer comprises a flange with a gapped region which enablesthe insert retainer to resiliently bend or deflect to pass of the headretainer.
 15. The method of claim 13, wherein the one or more tabs ofthe insert are flexible.
 16. The method of claim 13, wherein the insertcomprises threads and the head portion of the fastener comprises threadsthat engage one another.
 17. The method of claim 13, wherein the inserthas an upper diameter that is greater than a lower diameter of theinsert.
 18. The method of claim 17, wherein at least a portion of theinsert is ramped or tapered to create the different diameters.
 19. Themethod of claim 13, wherein the one or more tabs are compressed as theinsert is inserted through the aperture of the implant.
 20. The methodof claim 19, wherein the one or more tabs expand following compressionas the insert is inserted further down the aperture of the implant.